the intensity of the red color formed is proportional to the lactate concentration, the assay, using a set of lactate standards, can measure the concentration of lactate released to the culture medium, circulation, or urine in a quantitative manner. The non-radioactive assay kit allows the assay to be completed in one step within 30-60 min. The kit can be used for clinical samples such as serum, plasma, and urine (no TCA treatment is required). Each kit is sufficient for 200 (A-108S) or 400 (A-108L) assays using the 96-well format. The assay can be scaled up for spectrophotometric measurements. The only equipment required is a spectrophotometer or a microplate reader. See LDH Assay Kit. The method is adaptable to automation. Lactate dehydrogenase (LDH) is an oxidoreductase which catalyzes the interconversion of lactate and pyruvate. It consists of 4 subunits which may be of 2 different types: M (muscle) and H (heart), formerly known as A and B respectively. Five different isoenzymes are therefore possible, depending on the subunit composition. LDH is most often measured to evaluate the presence of tissue or cell damage. The non-radioactive colorimetric LDH assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased LDH activity. The superior sensitivity of the non-radioactive assay kit allows the assay to be completed within 20-30 min with minimal pipetting steps. Each kit is sufficient for approximately 200 assays using the 96-well format. See related product Lactate Assay Kit. The method is adaptable to automation. Alcohol dehydrogenase (ADH) together with mitochondrial aldehyde dehydrogenase are responsible for metabolizing the bulk of ethanol present in our diets. The enzymes are expressed at highest levels in liver, but at lower levels in other tissues. At least six different classes of mammalian ADHs have been described, and most are common to humans, mammals, and many vertebrates. Our non-radioactive colorimetric ADH assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased ADH activity. The kit is stable for at least one year under proper storage and handling conditions. The assay is simple, non-radioactive, and very sensitive. Each kit is sufficient for 200 microassays. The product is for research use only. In mammals, ethanol is metabolized mainly in the liver by alcohol dehydrogenase (ADH), which oxidizes ethanol to acetaldehyde. Acetaldehyde, a toxic metabolite responsible for the miserable effects of hangovers, is further oxidized to acetate by aldehyde dehydrogenase (ALDH). ALDH belongs to a large family of aldehyde dehydrogenases that can be found in many tissues of the body, but are at the highest concentrations in the liver. ALDH1 and ALDH2 display different abilities to detoxify small aldehydes (such as acetaldehyde) and large aldehydes (such as retinaldehyde). The assay solution uses acetaldehyde as a substrate, and thus preferentially detects the activity of ALDH2 in crude extracts. This non-radioactive colorimetric assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction. The INT reaction product is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased ALDH activity. The enzyme assay solution should be kept at -80ºC, and will remain stable at -80ºC for ~1 year. The product is for research use only. D-lactate accumulation in body fluids indicates bacterial infection or metabolic abnormality, and detection of D-lactate is therefore of clinical value. Unlike L-lactate, which is present at mM levels in the circulation, D-lactate is usually too low to be detected in healthy subjects. The D-Lactate Assay Kit is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which exhibits an absorption maximum at 492 nm. The D-Lactate Assay kit can measure the concentration of D-lactate present in serum or plasma with a detection limit of ~10 uM. Sample pretreatment with TCA or PCA is not required. Assay solutions are stable for at least one year if stored properly. Keep solutions at -80ºC for long term storage (more than 3 months). The product is for research use only. The ability to rapidly perform quantitative measurements of ethanol is highly desirable in life science research, clinical evaluations, and food and drug industries. Our non-radioactive colorimetric ethanol assay, which can be completed in 30-60 min, is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased ethanol concentrations (up to 0.5%). The kit is stable for at least one year under proper storage and handling conditions. The assay is simple, non-radioactive, sensitive, and can be adapted for automation. Each kit is sufficient for 200 microassays. The product is for research use only. Glucose-6-phosphate dehydrogenase (G6PD), a soluble enzyme, catalyzes the rate-limiting and regulated step in the pentose phosphate pathway, oxidizing glucose-6-phosphate with the production of NADPH, which is required for reductive biosynthesis and cellular defense against microbial pathogens and reactive oxygen species. The enzyme is particularly important for maintaining the integrity of red blood cells, and thus defective G6PD can cause hemolytic anemia in the presence of several precipitating factors (favism and infection). This non-radioactive colorimetric G6PD assay is based on the reduction of the tetrazolium salt INT in a NADPH-coupled enzymatic reaction. The INT reaction product is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased G6PD activity. The assay solution should be kept at -80ºC for long-term storage (more than 1 month), and will remain stable indefinitely at -80ºC. The product is for research use only. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a glycolytic enzyme mediating the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphate glycerate with the production of NADH. Although this house-keeping gene is often used as internal control for RNA and protein analysis, expression of the gene can be altered under certain cell growth and differentiation conditions. In addition, a switch from aerobic metabolism to anaerobic glycolysis may also be accompanied by a change in GAPDH expression. The GAPDH enzyme activity assay kit can be used to quickly assess potential changes in the expression of the gene. The non-radioactive colorimetric GAPDH assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased GAPDH activity. The kit is stable for at least one year if handled and stored properly. The product is for research use only. Glutamate dehydrogenase (GLDH), an important mitochondrial matrix enzyme integrating carbon and nitrogen metabolism, catalyzes the reversible oxidative deamination of L-glutamate into free ammonia and alpha-ketoglutarate in all tissues. Since the forward reaction generates a TCA cycle intermediate, GLDH is involved in energy homeostasis. In addition, kidney GLDH participates in acid/base balance of blood by release of ammonia. In clinical diagnostics, increased circulating levels of GLDH signal toxic or hypoxic liver damage. Our non-radioactive colorimetric GLDH assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased GLDH activity. The assay is simple and non-radioactive. Each kit is sufficient for 200 microassays. The assay solution should be kept in aliquots at -80ºC, and will remain stable indefinitely at -80ºC. The product is for research use only. Glucose, being a major energy source in most eukaryotic and prokaryotic organisms, is subject to tight metabolic regulation. In humans, glucose homeostasis under different metabolic circumstances is of vital importance, and insulin regulates the concentration of glucose in the blood such that its concentration normally falls within the 3.5-8 mM range. Abnormal circulating levels of glucose are associated with several pathologic states such as diabetes and obesity. Aerobic and anaerobic glucose metabolic pathways convert glucose to acetyl-CoA and lactic acid, respectively, which are differentially adopted by different tissues. Cell culture media typically contain high levels of glucose (5-25 mM), which promotes lactic acid formation and secretion in culture. The Glucose Assay Kit is based on sequential hexokinase and glucose-6-phosphate dehydrogenase reactions in a NADP+-coupled oxidation-reduction, which generates formazan exhibiting an absorption maximum at 492 nm. The Glucose Assay kit is used to measure the concentration of glucose present in diluted serum and cell culture media with a linear detection range of 0.1 – 1 mM. Sample pretreatment with TCA or PCA is not required. The assay solution is stable for at least one year, and should be kept at -80ºC for long term storage (more than 1 month). Hexokinase catalyzes the first step of glycolysis, converting glucose to glucose-6-phosphate. There are four mammalian hexokinase isoforms (I, II, III, and VI) that differ in tissue distribution and catalytic kinetics. Hexokinase I, II, and III exhibit a low Km for glucose whereas hexokinase IV (glucokinase) has a Km for glucose 100 times higher than that of other hexokinase. The hexokinase assay solution contains 20 mM glucose, and thus measures the total hexokinase activity of crude cell or tissue extracts. This non-radioactive colorimetric assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction. The INT reaction product is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased hexokinase activity. The enzyme assay solution should be kept at -80ºC for long-term storage (more than 1 month), and will remain stable indefinitely at -80ºC. Luciferase encoded by the firefly luciferase gene is widely used as a sensitive reporter enzyme for the study of transcriptional regulation. The enzyme catalyzes, in the presence of ATP (see ATP Assay Kit), the oxidation of luciferin with concomitant emission of yellow-green light, which can be conveniently measured by scintillation counters or luminometers. Light emission peaks in several seconds at 560 nm when the reaction is conducted at pH 7.8 (Anal. Biochem. 80:496,1977). The rapid appearance and decay of the light flash require consistent timing of the light measurement to obtain reliable data. This provides the basis for an assay system many times more sensitive than the b-galactosidase (GAL) or other reporter gene systems (PNAS USA 82:7870,1984 & Mol. Cell. Biol. 7:725,1987). The luciferase-based reporter assay is thus well suited for those cell systems exhibiting low transfection efficiency. The kit is sufficient for 200 assays using 0.1 ml of Luciferase Substrate per assay. Reconstituted Luciferase Substrate solution if stored in aliquots at -75°C is stable for at least one year. Repeated freeze-thaw cycles should be avoided. Isolation of high-quality plasmid DNA from the gemisch of the E. coli cell lysate paves the way for many laboratory as well as clinical genetic applications, among which are clone screening, DNA sequencing, DNA transfection, probe preparation, PCR analysis, and gene therapy, to name but a few. Although small-scale plasmid purification (mini-prep) is often sufficient for DNA cloning and sequencing, large-scale (maxi-prep) plasmid purification is required for gene transfer and gene therapy studies. Our Maxi-Plasmid Isolation Kit is similar to the Mini-Plasmid Isolation Kit with additional filtration and precipitation steps. Plasmid DNA can be easily and rapidly purified without the use of phenol. Each Maxi-prep DNA is purified from 100 - 200 ml of overnight E. coli culture in 90 min with a typical yield of 0.5 – 3 ug DNA (as determined by plasmid replication origin) per ml of culture. Purified plasmid DNA, typically with an A260/A280 ratio of ~2, is suitable for restriction digestion, probe preparation, DNA sequencing, PCR analysis, and transfection. The kit (sufficient for 10 maxi-preps) is stable for at least one year if handled and stored properly. Pyruvate is the end product of aerobic glycolysis and is at an important metabolic crossroad. The pyruvate dehydrogenase multi-enzyme complex (PDH) catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA in a series of reactions mediated by the E1 subunit (pyruvate dehydrogenase), E2 subunit (dihydrolipoyl transacetylase), and E3 subunit (dihydrolipoyl dehydrogenase). The reactions of the PDH complex serve to interconnect the metabolic pathways of glycolysis, gluconeogenesis and fatty acid synthesis to the Krebs (TCA) cycle. As a consequence, the PDH complex is highly regulated by a variety of allosteric effectors and by covalent modification. The importance of the PDH complex in metabolic regulation is evident from the fact that although diseases associated with deficiencies of the PDH complex have been observed, affected individuals often do not survive to maturity. This non-radioactive colorimetric PDH assay is based on the reduction of the tetrazolium salt INT in a NADH-coupled enzymatic reaction to formazan, which is water-soluble and exhibits an absorption maximum at 492 nm. The intensity of the red color formed is increased in the presence of increased PDH activity. One of the most widely used enzymes for chromogenic detection in immunoassays is horse-radish peroxidase (HRP), an extremely stable enzyme (Clin. Chim. Acta 81:1,1977). The substrate 3,3',5,5'-tetramethylbenzidine (TMB) has emerged as the safest colorigenic substrate of HRP exhibiting excellent sensitivity (Tetrahedron 30:3299,1974), and is thus often used in enzyme-linked immunosorbent assay (ELISA). The ELISA TMB substrate develops a blue color in the presence of HRP and peroxide. The blue color can be converted to a yellow color with an absorption maximum at 450 nm upon reaction termination by acidification.